A laser module including a plurality of laser diodes is widely used as a light source for outputting a laser beam. Documents disclosing such a laser module include, for example, Patent Literature 1.
Patent Literature 1 discloses a laser module 10 which, as illustrated in FIG. 8, includes (1) a group of laser diodes LD that generates a first beam bundle consisting of laser beams whose optical axes are aligned parallel to one another in a first plane and whose F axes are orthogonal to the first plane, (2) a group of collimating lenses C that collimates a divergence, in an F-axis direction, of each of the laser beams constituting the first beam bundle generated by the group of laser diodes LD, (3) a group of mirrors M that converts the first beam bundle, which is constituted by the laser beams the divergence of each of which in the F-axis direction has been collimated by the group of collimating lenses C, into a second laser beam bundle consisting of laser beams whose optical axes are aligned parallel to one another in a second plane and whose F axes are parallel to the second plane, (4) a converging lens L that converges the second beam bundle by refracting, in the second plane, the laser beams constituting the second beam bundle obtained with use of the group of mirrors M, and (5) an optical fiber OF that receives the second beam bundle converged by the converging lens L.
Each double mirror Mi constituting the group of mirrors M is constituted, as illustrated in FIG. 9, by a first mirror Mi1 that reflects each laser beam constituting the first beam bundle and a second mirror Mi2 that reflects the laser beam reflected by the first mirror. In the laser module 10, (a) adjusting an orientation of the first mirror Mi1 of each double mirror Mi (causing minute rotation of the first mirror Mi1 around a z axis as a rotation axis) allows a traveling direction of a corresponding laser beam of the second beam bundle to be changed in an elevation angle direction and (b) adjusting an orientation of the second mirror Mi2 of each double mirror Mi (causing minute rotation of the second mirror Mi2 around a z axis as a rotation axis) allows a traveling direction of a corresponding laser beam of the second beam bundle to be changed in an azimuth direction. Accordingly, even in a case where traveling directions of the laser beams constituting the first beam bundle that enters the group of mirrors M vary, adjusting the orientations of the first mirror Mi1 and the second mirror Mi2 of each double mirror Mi allows obtaining a second beam bundle consisting of laser beams that do not vary in traveling direction.
However, in a case where the second beam bundle is a parallel bundle (a set of laser beams whose optical axes are parallel to one another) at a portion where the second beam bundle has not been converged by the converging lens L as illustrated in FIG. 8, laser beams constituting the second beam bundle at a portion where the second beam bundle has been converged by the converging lens L do not intersect with one another, as illustrated in (a) of FIG. 10. This is because the converging lens L has spherical aberration. This makes it difficult to cause all of the laser beams constituting the second beam bundle to enter the optical fiber OF. Accordingly, an efficiency of coupling between the group of laser diodes LD and the optical fiber OF decreases.
Technologies that address the above situation are disclosed in documents including, for example, Patent Literature 2. Patent Literature 2 discloses the following matters. Specifically, in a case where, as illustrated in (b) of FIG. 10, a beam bundle is a convergent bundle (a set of laser beams whose optical axes are spaced apart from one another by a distance that decreases as a distance from a light source increases) at a portion where the beam bundle has not been converged by a converging lens, the laser beams constituting the beam bundle at a portion where the beam bundle has been converged by the converging lens successfully intersect with one another at a single point. Further, in a case where, as illustrated in (c) of FIG. 10, a beam bundle is a divergent bundle (a set of laser beams whose optical axes are spaced apart from one another by a distance that increases as a distance from a light source increases) at a portion where the beam bundle has not been converged by a converging lens, the laser beams constituting the beam bundle at a portion where the beam bundle has been converged by the converging lens successfully intersect with one another at a single point.
A laser module that utilizes the technology disclosed in Patent Literature 2 is disclosed in documents including, for example, Patent Literature 3. Patent Literature 3 discloses a laser module 20 which, as illustrated in FIG. 11, is obtained by adjusting an orientation of the second mirror Mi2 of each double mirror Mi of the laser module 10 of Patent Literature 1 so that the second beam bundle is a convergent bundle at a portion where the second beam bundle has not been converged by the converging lens L. This allows laser beams constituting the second beam bundle at a portion where the second beam bundle has been converged by the converging lens L to intersect with one another at a single point. Accordingly, it becomes possible to increase an efficiency of coupling between the group of laser diodes LD and the optical fiber OF as compared with the laser module 10 disclosed in Patent Literature 1.